A record-setting heatwave is forecast to hit cities in the southwestern US, with temperatures expected to reach 117°F in Las Vegas and a scorching 120°F in Phoenix. Authorities are anticipating this heatwave to be so severe that American Airlines has already canceled 38 flights for Tuesday out of the Sky Harbor International Airport as a precaution.

For those unfortunate enough to have a seat booked on one of the cancelled flights, the airline is allowing Phoenix passengers scheduled to fly during the peak heat Monday through Wednesday to change their flights without incurring a fee. The soaring temperatures will have their biggest impact on small regional jets departing from Phoenix, as it will change the air density, making it harder for airplanes to take off.

Usually to counter the problems faced during departure, airlines will impose weight restrictions that they enforce by carrying less cargo and fuel. According to David R. Harwell, a spokesman for the City of Phoenix Aviation Department, the runways are able to accommodate aircraft taking off in extreme conditions, however, the final decision of whether to ground flights or not ultimately falls on the individual airlines.

According to a statement released by American Airlines, all aircraft have a maximum operating temperature, with those manufactured by Airbus having the highest of any of their planes at 127°F. “The heat is expected to impact some of our regional flights, operated by Mesa Airlines and SkyWest Airlines, especially on Tuesday, June 20,” the statement says. “American Eagle (our regional flights), operated by Mesa and SkyWest, operate the CRJ aircraft to/from PHX. On average, American Eagle has 90 departures and 90 arrivals daily.”

The CRJ aircraft only has a maximum operating temperature of 118°F so American Airlines has canceled 20 regional flights for Tuesday due to the extreme heat. Despite these setbacks, Harwell still claims that the Sky Harbor airport is “well prepared for Arizona summers,” with airport employees being asked to take frequent breaks and to stay hydrated. Air-conditioned trailers are also being set up on the airfield so maintenance workers can take a break in comfort.

Phoenix has not seen temperatures reach 120°F in over 20 years, with the all-time high being set on June 26, 1990, when the mercury soared to 122°F. Some flights out of Sky Harbor were cancelled that day, not only due to aircraft not being able to handle the conditions, but also because the airport’s runway at the time was made from asphalt, which started to become soft and melt.